1. Field of the Invention
The present invention relates to curable adhesive and sealant compositions in a dry-to-the-touch form. More particularly, the present invention relates to dry-to-the-touch adhesive and sealant compositions which are particularly useful in threadlocking and sealing applications and may include various product forms of the compositions including dry-to-the-touch tapes and gaskets.
2. Brief Description of Related Technology
It is common practice in the use of threaded mechanical fasteners, such as nut/bolt assemblies, to apply to one or more of the threadable engagement surfaces thereof an adhesive/sealant composition, termed a threadlocking composition, for the purpose of locking and/or sealing the constituent members of such fasteners when they are engaged in their final interlocked state.
Such threadlocking compositions significantly increased the torque required to break or turn the engaged threaded members. Conventional threadlocking compositions oftentimes include co-reactive adhesive systems. With this type of threadlocking composition, two or more components are mixed before applying the resulting composition to the threaded engagement surface(s) of the fastener on which the components in the threadlocking composition react to cure. Examples of such co-reactive systems include epoxy resin adhesive compositions.
Liquid adhesive compositions have long been used in sealing and threadlocking applications and have become a standard part of assembly production as well as in the maintenance of machinery, tools and the like. Among the liquid adhesive compositions commonly used in these applications are anaerobic compositions. These compositions provide excellent threadlocking and sealing properties when cured and that remain stable, and thus in liquid form, until they are placed between parts where they cure in the absence of air. Moreover, these compositions remain stable for long periods of time during storage in the bottle.
In many situations, the ability of the liquid adhesive composition to migrate from parts is problematic, causing contamination in the general vicinity, as well as contamination of the environment. One attempt to create a convenient ready-to-use threadlocking product has been the use of preapplied adhesive compositions, such as those in micro-encapsulated form. In such cases, the adhesive composition is applied to the threaded part, such as a bolt or nut, and remains in the uncured state until mated. Generally, in this case, components which would cause premature curing of the unmated part are kept separated from other components by encapsulation. The mating of the parts causes rupture of the encapsulation casing, thereby releasing the components for cure.
Compositions that are applied to parts just before mating have also relied on wax or wax-like matrices into which anaerobic curable resins are incorporated. While such compositions are easy to apply and have certain advantages, such as non-flowability due to their rheological properties, they are not dry-to-the-touch. Moreover, such compositions generally lose their non-flowable nature once certain temperatures are exceeded, such as 180° F. or in some cases involving polyamide matrices those temperatures may reach 260° C. (500° F.) before that happens, and thus lose their advantage over pre-applied or traditional liquid thread lockers since at these temperatures migration begins to occur. Moreover, the wax or wax-like matrices have been described as being used in significantly smaller amounts than the anaerobic component such as amounts of up to about 20% by weight of the total compositions.
While preapplied coatings have many advantages, special processing is sometimes required to prepare and apply the adhesive coatings in advance. Such compositions are not always useful on an as-needed basis, such as when an immediate need for application of a curable composition is required. For instance, it may be necessary to stock and inventory different sizes of pre-applied coated parts in advance. Thus, pre-applied coatings do not solve the problem for many applications requiring ready-to-use compositions.
Though conventional anaerobic threadlockers have been and remain well-received in the marketplace, there are shortcomings for certain commercial applications that have been observed with the use of conventional liquid anaerobic threadlockers, as well as known non-flowable, thixotropic anaerobic-based threadlockers. For instance, oftentimes such compositions do not fully cure through large gaps. Also, because of their nature of anaerobic cure, portions of the adhesive which remain exposed to air once applied to the parts will have difficulty curing (absent a secondary cure mechanism that is triggered). Thus, external bondlines which remain exposed to air on a nut/bolt assembly oftentimes will remain liquid unless additional additives and cure measures are taken to ensure cure. As a result, liquid compositions at the external bondlines tend to migrate. In the case of conventional non-flowable compositions, which depend on the thixotropic and/or rheological properties of the composition for their non-flowability, these compositions will flow if the temperature to which they are exposed is high enough. Additionally, the resistance to solvents of cured products (that have portions which remain uncured, as noted above) may be poor, indicative of questionable integrity when environmental interaction occurs. This may lead to contamination problems and hazardous conditions for the surroundings.
It would be extremely useful and a significant advance in the field of reactive threadlockers and sealants, to provide a reactive formulation useful for threadlocking applications, which overcomes the disadvantages of known compositions. It would also be highly advantageous to provide a cost effective dry-to-the-touch, easy to apply composition, as an alternative to such known threadlocking compositions.